It is often necessary to introduce treatment chemicals into fluid producing wells in order to correct or prevent certain undesirable conditions. Corrosion or scale inhibitors, for example, have been introduced in a variety of ways in both solid and liquid form. One method of introduction involves pumping or pouring chemicals in liquid form down the tubing string or the production string, or through separate strings of tubing inserted into the well bore for that purpose. Although chemicals in liquid form can be readily mixed with the flow of production fluids and can be readily pumped or poured at controlled rates, there are serious disadvantages to the use of these treatment methods. The use of additional strings of tubing is expensive and runs the risk of interfering with other operations of the well, while the pumping or pouring of liquid chemicals from the surface down into the well can require an excess of chemicals to be introduced, at a correspondingly higher cost, in order to ensure adequate distribution throughout the well.
Both solid and liquid treatment compositions have also been introduced from containers which are filled with chemicals on the surface and lowered into the well. A number of ways have been suggested for introducing the chemicals into the production fluid from the containers. Containers which are degradable by the treatment composition or by the well fluid have been used. While overcoming some of the objections to the continuous pumping or pouring of liquid chemicals referred to above, there are distinct disadvantages to this approach as well. Some methods of introducing the containers and releasing the chemicals require temporary interruption of well production, while most methods of chemical release are not able to continuously inject controlled amounts of treatment chemicals into the production fluid. The result has been the introduction of chemicals basically in the form of a batch treatment process, with accompanying lack of adequate control over the operation.
Although one method of introducing chemicals from a container, described in U.S. Pat. No. 2,635,996, involves a relatively slow continuous release into the production fluid, this method is able to introduce chemicals only over a relatively short period of time, such as 24 hours. Thus this method in effect constitutes simply another variation of a batch-type introduction process. Moreover, it requires the use of a chemical composition in solid form, which is not preferred from the standpoint of its ability to readily mix with the production fluid and the ability to control the rate at which the chemicals are introduced.
Another way of introducing liquid treatment chemicals involves the use of containers which incorporate various types of arrangements for causing the release of chemicals carried by the containers. For example, pistons, bellows, pumps and the like have been incorporated in the design of containers for injecting or pumping treatment liquid into the well. While enabling some control over the rate at which the liquid is introduced, these mechanical arrangements are generally relatively complicated in design, resulting in costly containers, a higher probability of failure than desired and a relatively short operating life.
It would be desirable to be able to introduce chemical treatment fluids into a well bore from a container in an accurate, controlled and reliable manner, and to do so with a system which is simple, uncomplicated and inexpensive. Further, it would be highly desirable to be able to accomplish the foregoing with a system which can introduce treatment fluids over a relatively long period of time.